Enable Python 3.15 / 3.15t for Windows wheel builds

Extend the opt-in preview Python versions (INCLUDE_PREVIEW_PYTHON_VERSIONS) to
Windows so 3.15 / 3.15t are generated for Windows wheels, matching the Linux
and macOS enablement. The interpreter setup (conda-forge python_dev/python_rc
labels) is shared across OSes via .github/actions/setup-binary-builds.

The Windows smoke test still runs for 3.15 / 3.15t, but installs the built wheel
with --no-deps: numpy has no cp315 Windows wheel yet and cannot build from
source in the env. torch is already installed, so the torch import smoke test
still runs.

Also update the matrix unit tests (Windows now opts in).

Authored with assistance from Claude Code (AI assistant).

Author: atalman

.github/workflows/build_wheels_windows.yml

@@ -362,7 +362,14 @@ jobs:
           source "${BUILD_ENV_FILE}"
           WHEEL_NAME=$(ls "${{ inputs.repository }}/dist/")
           echo "$WHEEL_NAME"
-          ${CONDA_RUN} pip install "${{ inputs.repository }}/dist/$WHEEL_NAME"
+          # numpy has no cp315 Windows wheel yet and cannot build from source, so
+          # install without deps for 3.15 to keep the smoke test running (torch is
+          # already installed in the env).
+          if [[ "${{ startsWith(matrix.python_version, '3.15') }}" == "true" ]]; then
+            ${CONDA_RUN} pip install --no-deps "${{ inputs.repository }}/dist/$WHEEL_NAME"
+          else
+            ${CONDA_RUN} pip install "${{ inputs.repository }}/dist/$WHEEL_NAME"
+          fi
           if [[ ! -f "${{ inputs.repository }}"/${SMOKE_TEST_SCRIPT} ]]; then
             echo "${{ inputs.repository }}/${SMOKE_TEST_SCRIPT} not found"
             ${CONDA_RUN} "${{ inputs.repository }}/${ENV_SCRIPT}" python -c "import ${PACKAGE_NAME}; print('package version is ', ${PACKAGE_NAME}.__version__)"

tools/scripts/generate_binary_build_matrix.py

@@ -454,14 +454,14 @@ def generate_wheels_matrix(
         # Define default python version
         python_versions = list(PYTHON_ARCHES)
 
-        # Opt-in preview versions (e.g. 3.15/3.15t) are torch-only and validated
-        # on Linux x86/aarch64 and macOS arm64. Append them to the default list
-        # so the shared default (used by domain libraries and Windows) is
+        # on Linux x86/aarch64, macOS arm64 and Windows. Append them to the
+        # default list so the shared default (used by domain libraries) is
         # unaffected.
         if include_preview_python_versions and os in (
             LINUX,
             LINUX_AARCH64,
             MACOS_ARM64,
+            WINDOWS,
         ):
             python_versions += PREVIEW_PYTHON_ARCHES_DICT.get(channel, [])
 

tools/tests/test_generate_binary_build_matrix.py

@@ -150,10 +150,15 @@ def _test_channel_python_versions(
         return {entry["python_version"] for entry in out["include"]}
 
     def test_preview_python_versions_opt_in(self):
-        # 3.15 / 3.15t are validated on Linux x86/aarch64 and macOS arm64 for the
-        # nightly and test channels when explicitly opted in.
+        # 3.15 / 3.15t are validated on Linux x86/aarch64, macOS arm64 and Windows
+        # for the nightly and test channels when explicitly opted in.
         for channel in ("nightly", "test"):
-            for operating_system in ("linux", "linux-aarch64", "macos-arm64"):
+            for operating_system in (
+                "linux",
+                "linux-aarch64",
+                "macos-arm64",
+                "windows",
+            ):
                 versions = self._test_channel_python_versions(
                     operating_system, include_preview="enable", channel=channel
                 )
@@ -167,14 +172,6 @@ def test_preview_python_versions_off_by_default(self):
             self.assertNotIn("3.15", versions)
             self.assertNotIn("3.15t", versions)
 
-    def test_preview_python_versions_excluded_on_windows(self):
-        # Windows must not pick up the preview versions even when opted in.
-        versions = self._test_channel_python_versions(
-            "windows", include_preview="enable"
-        )
-        self.assertNotIn("3.15", versions)
-        self.assertNotIn("3.15t", versions)
-
     def test_preview_python_versions_excluded_on_release_channel(self):
         # Preview versions are defined for the nightly and test channels only,
         # never for the release channel.